There are a lot of ways to build a wall, as Donald Trump can attest.

Although it’s quite possible that even the president doesn’t fully grasp what a cadre of lawyers, policymakers and advisers are accomplishing on his behalf.

He’s simply too focused on his precious, magical wall at the Southern border.

Meanwhile, what’s happening to immigration law is incredibly destructive to people who wish to enter the nation legally. It is keeping people out.

The president is getting his wall. But this version is not a gargantuan physical barrier, suitable for photo ops as Trump winds up a re-election campaign.

Nor will these impacts be widely publicized during round two of negotiations between the president and Congress, as they squabble over Trump’s demands for $5.7 billion to satiate his obsession.

Rather, Trump’s will is being done through a complicated set of policies, processes and protocols that govern how our immigration system functions. It’s a matter of paperwork and the rules that govern that paperwork.

Slowly, the Trump administration has been making it increasingly difficult for a wide range of immigrants to gain or retain their legal status. College students here on visas have been affected, as have high- and low-tech workers, and naturalized U.S. citizens who merely wish to reunite with family members.

Bit by bit, tweak by tweak, this is occurring.

A prime target has been Central Americans wishing to apply for asylum. They’re proving an easy target.

The administration attempted to change who is allowed to seek asylum, undercutting those who are escaping domestic and gang violence. Standards of proof were shifted, raising the bar for proof that a person faces a credible threat of being persecuted in his or her native land, which is the first step to becoming a refugee.

Protections for fairness have been whittled away, especially those allowing asylum-seekers access to legal counsel.

The latest is the scheme to force Central American migrants to remain in Mexico while they await their chance to plead their case before an immigration judge.

The Department of Homeland Security first floated this idea in December. In late January, they rebranded it, with typical doublespeak, as “Migrant Protection Protocols.” DHS insists the protocols are merely a pilot program, giving the perception that it could be temporary, easily dismantled if things don’t go as planned.

Literally, this is casting humans back across the Southern border like chum. They’ll be in no man’s land, having fled one country and trapped between two others.

Unknown is how far Mexico will play along. So far, Mexican migration officials have reacted by claiming that they will do right by the Central Americans because accepting them into the country, even temporarily, is the humanitarian thing to do.

Immigrants’-rights activists will likely challenge the new policies in court, as they have challenged other gambits by the Trump administration. It’s proving a never-ending battle.

To some, many of the changes amount to a barely noticeable rewrite of immigration law. But the results can be devastating. Meanwhile, Trump has consistently degraded immigrants, particularly Central Americans.

Americans who understand immigration law as strict polar opposition between “legal” or “illegal” might be surprised to learn how they are being duped.

We the people control who is allowed to be legal or not by how we manage the rules. It’s possible to eliminate whole categories of people from entry, no matter how much they try to “do it the legal way.”

Undoing long-existing immigration law has been at the top of the Trump administration’s agenda. And unless more people start to pay attention, it will take us decades to reclaim our moral, legally codified high ground, if we ever do.